Why isn't there a protective screen with large diameter holes (approx 2') mounted in front of the jet engine intake to protect the turbine blades? This would keep larger birds and large ground debris from getting sucked in, which can cause serious internal engine damage.

$\begingroup$Would the filter really prevent the birds to go inside the engine, considering the energy of the impact?$\endgroup$
– minsApr 23 '15 at 21:33

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$\begingroup$What sort of screen are you imagining? It's hard to save a bird when the relative velocity is 300 mph.$\endgroup$
– raptortech97Apr 23 '15 at 22:47

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$\begingroup$@raptortech97 I think the goal is to protect the engine from the bird, not protect the bird from being hit by something at hundreds of miles per hour.$\endgroup$
– David RicherbyApr 24 '15 at 14:36

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$\begingroup$If you did have a screen, what's going to happen when the bird hits it? The suction from the engine isn't going away, since you don't want to shut the engine down in flight. Either the bird will get sucked through the screen in pieces and go into the engine anyway, or it will get stuck on the screen and disrupt the flow of air, which seems like it might be a problem.$\endgroup$
– Nate EldredgeApr 24 '15 at 15:40

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$\begingroup$One also has to wonder whether the mesh can actually save an engine. It obviously cannot keep the bird out of the engine; all it can do is slice it up a bit before it hits the blades.$\endgroup$
– RomanApr 25 '15 at 23:32

5 Answers
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Modern high-bypass turbofan engines work by pulling in immense volumes of air and accelerating it. A screen as proposed would make that task far more difficult, which would ruin the efficiency of the engine. It's also pretty well unnecessary.

Jets worldwide take plenty of birdstrikes every day. Unless the pilots see it (hitting the windscreen will do that) or hear it (hitting something near the cockpit) or the bird goes into the engine core (which causes the smell of burned bird in the air conditioning), the chance that the crew knows about it before the next walk-around inspection is pretty slight. The vast majority of birdstrikes are utterly inconsequential. (Except for the bird -- ruins his day pretty thoroughly!)

Yes, there are a small number of very highly visible events where birds do disable an aircraft -- the "miracle on the Hudson" and the loss of an AWACS in Alaska come to mind, and there are others. And it's possible for a birdstrike on an engine to cause significant damage IF the bird is large enough AND it goes into the core, but in the big picture, that is actually pretty uncommon.

Thus, the aircraft manufacturers and operators end up accepting the risk of a catastrophic birdstrike, because the alternative of protecting the engine as suggested is too expensive when the effects on the efficiency of the engine are considered.

One other point, bird flesh is pretty easy for an engine to chop up and digest. If a big bird hits a metal shield at high speed, there would be the risk that the shield could be damaged enough that some of the metal would break apart and go into the engine as well, and THAT would cause far more damage than just the bird.

$\begingroup$well said and great videos$\endgroup$
– FreeManApr 24 '15 at 0:06

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$\begingroup$I think it's worth mentioning that decreasing the efficiency of the engines is itself a safety risk. Less power for hot days, short runways, collision avoidance maneuvers, etc.$\endgroup$
– Wayne ConradApr 24 '15 at 3:32

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$\begingroup$more important I think is that it wouldn't really do much good. The screen would just turn the bird into chunks of bird. While that might prevent a bent fan blade at the first low pressure fan, maybe, it wouldn't do much more.$\endgroup$
– jwentingApr 24 '15 at 7:43

$\begingroup$So we notice the bird if we see it, hear it, or smell it. Hopefully there's not to many documented cases of a flight crew noticing the bird via taste or touch!$\endgroup$
– Cort AmmonJun 15 '18 at 18:52

$\begingroup$It's probably also worth noting that, while the big surface of the sphere reduces aerodynamic loss in the case of a test fixture that is stationary with respect to the air around it, it would cause an incredible amount of drag were it actually moving through the air.$\endgroup$
– reirabApr 24 '15 at 15:55

$\begingroup$The screen in the second picture isn't really to block FOD, but it does have that added benefit.$\endgroup$
– fooot♦Apr 26 '15 at 0:03

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$\begingroup$Doesn't that show the danger of ingesting bubble gum while running in reverse?$\endgroup$
– NobodySpecialApr 26 '15 at 2:32

A few Russian/Soviet fighters had retractable FOD screens on their engine intakes (MiG-29 and Su-27 IIRC). The assumption was that they would operate from damaged runways or roads and the engines would need protection against Foreign Object Damage (FOD).

Right air intake of a MiG-29 with main doors closed and louvres on the wing root opened.

$\begingroup$Mind that these were not intended for operation in flight. They are only operated during takeoff and landing, they restrict the airflow too much to be practical during regular operations (the performance of the aircraft suffers too much) or even when taking off at high weight.$\endgroup$
– jwentingApr 24 '15 at 7:41

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$\begingroup$Nor are they designed to take a bird at cruise speed.$\endgroup$
– cpastApr 25 '15 at 22:22

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$\begingroup$Do you encounter many birds at cruise ? I thought they were mainly a danger during take off and landing. You don't do much bird spotting at 40,000ft$\endgroup$
– NobodySpecialApr 26 '15 at 2:31

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$\begingroup$Depends on your mission profile. The MiG-29 was designed primarily as an air-superiority fighter (originally the answer to the F-15, itself developed in direct response to the MiG-25), but was adapted to multirole use especially with the M variant; air-to-ground mission profiles even for deep strikes often involve relatively low-altitude cruising.$\endgroup$
– KeithSApr 27 '15 at 19:57

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$\begingroup$@NobodySpecial that would depend on your routing. Flights are rerouted during bird migration season to avoid high altitude flocks for a reason. There are birds that high up, just not many.$\endgroup$
– jwentingMay 2 '15 at 15:21

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